This invention relates to ternary pulse transmission and, more particularly, to noise suppression circuitry for ternary pulses.
Ternary pulse signals assume one of three states, namely, a state represented by a positive pulse, a state represented by a negative pulse, and a state represented by no pulse. In telephony, ternary pulses are commonly employed to carry signals on the transmission lines and networks. For example, the well known T-carrier transmits telephone signals in pulse code modulation form on interoffice and short haul trunks originally installed for other types of carrier transmission systems or direct voice transmission. In a T-carrier system, a pulse in a time slot or bit position represents one binary value, and the absence of a pulse in a time slot or bit position represents the other binary value. Successive pulses alternate in polarity. Accordingly, one technique to monitor the performance of the system is to compare the polarity of successive pulses. Successive pulses of the same polarity indicate an error.
The limited bandwidth of transmission lines that carry ternary pulses gives rise to peak overshoot at the leading edge of the pulses, and baseline overshoot at the trailing edge of the pulses. In equalizing transmission lines, such overshoot is often introduced at the transmission end of the line. Baseline overshoot is particularly troublesome because it closely resembles the ternary pulses themselves. A discriminator may have difficulty distinguishing between baseline overshoot and information pulses if the baseline overshoot is nearly as large as the threshold level of the pulse discriminator.